1. Field of the Invention
The present invention generally relates to a motor drive circuit for use in combination with a motor driven apparatus such as, for example, an electrically driven tiltable door mirror provided externally on a body of a motor vehicle projecting laterally therefrom, wherein the housing of the tiltable door mirror is rotatably driven to a folded (retracted) position from a set (projecting) position or vice versa through a remote control from the interior of the motor vehicle.
2. Prior Art
As the outside mirror for a motor vehicle, there are known a fender mirror and a door mirror. The fender mirror has a reflecting surface implemented in the form of a convex mirror and is advantageous in that a large field of view can be assured with a relatively small size and hence the lateral projection of the mirror can be minimized. In contrast, in the case of the door mirror, the reflecting surface is implemented in the form of a plane mirror because the mirror is disposed at a position closer to the point of sight of a driver. Consequently, the door mirror is necessarily of a relatively large size. More specifically, referring to FIG. 1 of the accompanying drawings, the door mirror denoted by a reference character D for a motor vehicle is laterally mounted with a length of projection l. Consequently, space required for storing the motor car in a garage or for transportation thereof is correspondingly increased, involving other additional inconveniences. Besides, when the car is parking, the door mirror may be contacted by passers-by or other cars by accident to be damaged thereby.
For evading the disadvantages mentioned above, there have heretofore been adopted foldable structures of the door mirror which allows the mirror to be folded (retracted) so as to lie within the maximum width of the car body, when occasion requires. Further known in this connection are a manually foldable structure and an automatically foldable structure. In the former case, however, inconvenience is encountered in that the driver must get out of the car every time the door mirror is to be folded or extended, a troublesome labor particularly on a rainy day. This problem can be avoided in the case of the automatically operatable door mirror. In the hitherto known structures of such automatically manipulatable door mirrors, an electric motor is installed within a mirror housing as a drive power source, wherein the motor is rotated selectively in a forward or reverse direction to extend or retract the mirror through remote control from the interior of the car.
FIG. 2 of the accompanying drawings shows in a block diagram a motor drive circuit for the electromechanically tiltable door mirror known heretofore.
Referring to the figure, a motor 111 is disposed within a mirror housing and serves as the driving power source for positioning the door mirror in the folded storage state or in the extended (projecting) state. A motor drive circuit 112 in the form of an integrated circuit or IC is connected to the motor 111 and a power supply source Vcc. The motor drive circuit 112 is provided with switches 113 and 114 mounted on an instrumentation panel at respective positions so as to be easily manipulatable by a driver. Resistors 116 and 115 are connected between the power supply source Vcc and the switches 113 and 114 in parallel with the motor drive circuit 112. The other ends of the switches 113 and 114 are connected to the ground potential. The motor drive circuit also has an earth potential terminal.
So long as the switches 113 and 114 are opened, the motor 111 is not driven. When the switch 113 is closed with the switch 114 being opened, the motor 111 is rotated in the forward direction by the motor drive circuit 112, whereby the mirror housing is set to the laterally projecting position (also referred to the set position). On the other hand, when the switch 114 is closed with the switch 113 being opened, the motor 111 is rotated in the backward or reverse direction to cause the mirror housing to be moved to the retracted position (also referred to as the folded position). Further, when the motor 111 is to be stopped in the course of forward or reverse rotation, this can be accomplished by closing both switches 113 and 114 simultaneously.
As will be seen from the foregoing description, the hitherto known motor drive circuit requires two switches 113 and 114 for rotating the motor in forward and backward directions, respectively. In other words, the prior art mirror drive circuit is incapable of rotating the mirror drive motor selectively in the forward or backward direction with a single switch such as a push button switch. Besides, these known motor drive circuit are not of such structures which allow the duration of motor energization to be automatically controlled. Consequently, the driver must select the forward or reverse rotation switch as occasion demands and holds the selected one in the operated state for a predetermined time, a troublesome procedure.